U.S. patent application Ser. No. 862,352 filed Dec. 20, 1977 describes an improved heat exchanger for vaporization cooled transformers. The vaporization cooled transformers are of the type employing a low boiling point vaporizable fluid, such as trichlorotrifluoroethane, and a heat exchanger for allowing the vaporizable fluid to transfer its heat to the environment. The aforementioned U.S. Patent application improves over state of the art of heat exchangers by arranging the cooling tubes in a horizontal rather than vertical plane. It has been discovered, however, that the horizontal arrangement of cooling tubes, can present a problem with the flow rate and quantity of coolant. The provision of an inlet pipe within inlet manifold wherein the tubes are intentionally positioned at a slight angle for drainage into the entrance manifold can cause the returning vapor droplets to impede the flow of incoming vaporized coolant. This is especially noticeable both under conditions of transformer overload and when the transformer is first energized. Upon start-up conditions a large amount of vapor is rapidly generated and forced into the heat exchanger. The substantial flow of vapor can actually push the condensed liquid droplets back into the manifold rather than allowing the droplets to return. This situation is called "Liquid hold up" and can seriously decrease the amount of liquid returning to the transformer tank. When a sufficiently low quantity of liquid occurs in the tank a liquid level indicating switch becomes energized and the transformer becomes electrically disconnected from the line.
The purpose of this invention is to provide an improved heat exchanger arrangement wherein incoming vaporized coolant assists the flow of returning condensed coolant back to the transformer tank. The location and design of the inlet and return pipes to and from the heat exchanger prevent the coolant liquid level in the transformer tank from becoming seriously diminished.